Tag: VoidLinux

pcap_next_ex() blocks in Void Linux forever

My Void Linux is a virtual machine. I implemented a simple capturing packets program using libpcap, but found the program is blocked in pcap_next_ex():

(gdb) bt
#0  0x00007ffff7ad7763 in __GI___poll (fds=fds@entry=0x7fffffffe160, nfds=nfds@entry=1, timeout=-1)
    at ../sysdeps/unix/sysv/linux/poll.c:29
#1  0x00007ffff7f8309d in poll (__timeout=<optimized out>, __nfds=1, __fds=0x7fffffffe160) at /usr/include/bits/poll2.h:46
#2  pcap_wait_for_frames_mmap (handle=handle@entry=0x55555556eba0) at ./pcap-linux.c:5018
#3  0x00007ffff7f886f4 in pcap_read_linux_mmap_v3 (handle=0x55555556eba0, max_packets=1, callback=0x7ffff7f82bf0 <pcap_oneshot_mmap>,
    user=0x7fffffffe1f0 "\260\355VUUU") at ./pcap-linux.c:5577
#4  0x00007ffff7f8c6a2 in pcap_next_ex (p=<optimized out>, pkt_header=<optimized out>, pkt_data=<optimized out>) at ./pcap.c:505
......

The libpcap version in Void Linux is 1.9.1. After checking code, I found although I set timeout in pcap_open_live(), this value doesn’t take effect in set_poll_timeout:

    ......
    if (handlep->tp_version == TPACKET_V3 && !broken_tpacket_v3)
        handlep->poll_timeout = -1; /* block forever, let TPACKET_V3 wake us up */
    ......

I don’t have physical machine, so not sure this issue only happens in virtual machine or not.

Fix “cannot find libasan_preinit.o” issue in Void Linux

In my Void Linux, using clang with -fsanitize=address option is OK:

$ clang -std=c11 -fsanitize=address test.c
$

Whilst gcc reports following error:

$ gcc -std=c11 -fsanitize=address test.c
/usr/bin/ld: cannot find libasan_preinit.o: No such file or directory
/usr/bin/ld: cannot find -lasan
collect2: error: ld returned 1 exit status

The solution is to install libsanitizer-devel:

$ sudo xbps-install -Su libsanitizer-devel
$ gcc -std=c11 -fsanitize=address test.c
$

Check the linked libraries of executalbe file:

$ ldd a.out
    linux-vdso.so.1 (0x00007fff1a58b000)
    libasan.so.5 => /usr/lib/libasan.so.5 (0x00007fc1f0f02000)
    libc.so.6 => /usr/lib/libc.so.6 (0x00007fc1f0d3f000)
    libdl.so.2 => /usr/lib/../lib/libdl.so.2 (0x00007fc1f0d3a000)
    librt.so.1 => /usr/lib/../lib/librt.so.1 (0x00007fc1f0d2f000)
    libpthread.so.0 => /usr/lib/../lib/libpthread.so.0 (0x00007fc1f0d0e000)
    libstdc++.so.6 => /usr/lib/../lib/libstdc++.so.6 (0x00007fc1f0a99000)
    libm.so.6 => /usr/lib/../lib/libm.so.6 (0x00007fc1f0952000)
    libgcc_s.so.1 => /usr/lib/../lib/libgcc_s.so.1 (0x00007fc1f0938000)
    /lib/ld-linux-x86-64.so.2 (0x00007fc1f193d000)

Reference:
How to use gcc with sanitizers in Void Linux?.

Fix “Permission denied” issue when installing manual in Void Linux

Today, I built and installed concurrencykit in Void Linux. When opening manual, it prompted following errors:

$ man ck_pr_barrier
man: /usr/local/share/man/man3/ck_pr_barrier.3.gz: Permission denied
man: outdated mandoc.db contains bogus man3/ck_pr_barrier.3.gz entry, run makewhatis /usr/local/share/man
man: outdated mandoc.db lacks ck_pr_barrier(3) entry, run makewhatis /usr/local/share/man
man: ERROR: /usr/local/share/man/man3/ck_pr_barrier.3.gz: Permission denied

Check the permission of manual file:

$ ll /usr/local/share/man/man3/ck_pr_barrier.3.gz
-rw------- 1 root root 1057 Dec 23 20:07 /usr/local/share/man/man3/ck_pr_barrier.3.gz

It indeed lacked read permission. Check the original file permission under my folder:

$ ll doc/ck_pr_barrier*
-rw-r--r-- 1 nan nan 2212 Dec 23 17:59 doc/ck_pr_barrier
-rw-r--r-- 1 nan nan 1057 Dec 23 20:07 doc/ck_pr_barrier.3.gz

It had read permission. The solution is adding following field in /etc/sudoers via the visudo command:

Defaults umask = 022

Reference:
Did sudo behaviour change recently?.

Enable Pressure Stall Information (PSI) on Void Linux

There are two configurations for Pressure Stall Information (PSI) feature in kernel: CONFIG_PSI for supporting PSI or not and CONFIG_PSI_DEFAULT_DISABLED for diabling PSI or not. Check my Void Linux configurations:

$ zgrep PSI /proc/config.gz
CONFIG_PSI=y
CONFIG_PSI_DEFAULT_DISABLED=y

We can see PSI is disabled by default, and it will incur following errors:

$ cat /proc/pressure/cpu
cat: /proc/pressure/cpu: Operation not supported

To enable this feature, add “psi=1” for GRUB_CMDLINE_LINUX_DEFAULT in /etc/default/grub file:

$ cat /etc/default/grub
#
# Configuration file for GRUB.
#
......
GRUB_CMDLINE_LINUX_DEFAULT="loglevel=4 slub_debug=P page_poison=1 psi=1"

Then regenerating the grub configuration and reboot:

$ sudo grub-mkconfig -o /boot/grub/grub.cfg
Generating grub configuration file ...
Found linux image: /boot/vmlinuz-5.2.13_1
Found initrd image: /boot/initramfs-5.2.13_1.img
done
$sudo reboot

The PSI is enabled:

$ cat /proc/pressure/cpu
some avg10=0.00 avg60=0.00 avg300=0.00 total=890919

References:
Getting Started with PSI;
Where are the current kernel build options stored?;
grub.